The present invention relates to a memory cell for use in the storage of binary valued data in a digital computer. More particularly, the invention relates to a high speed dynamic memory cell comprising capacitive elements.
The trend in present day digital computers is to process data at ever-increasing speeds. In following this trend toward high speed operation, digital computer memory units have gradually undergone a change from relatively slow magnetic core devices to higher speed semiconductor devices.
Recent developments in the art have included a three-transistor MOS dynamic memory cell utilizing a voltage variable capacitor for enhancing the refresh operation in restoring charge which dissipated by leakages within the cell. It has also been proposed to employ a voltage variable capacitor to apply enhanced voltage to the gate of the MOS readout transistor to more fully turn on the readout transistor by effectively increasing its transconductance. Such developments have also been generally directed toward high speed MOS memory cells.
However, these memory cells still have inherent speed limitations in communicating stored charge information via an MOS transistor. The speed of an MOS transistor is severely limited by capacitance effects. Since read and write access time is dependent upon the switching speed of the transistor, this limitation becomes critical for a high speed memory operation.
Accordingly, a primary object of the present invention is to achieve a higher speed MOS dynamic memory cell.
It is a further object of this invention to reduce the amount of transistor switching required for communication of charge storage information in MOS dynamic memory cells.
In achieving the above-mentioned objects, the dynamic memory cell of the present invention provides a MOS voltage variable readout capacitor enabling readout of binary information in the form of stored charge at a storage node comprising the common junction of a fixed access capacitor and a MOS device which determines the value of charge to be written into the storage node.